By Shanna Daniel, Archaeological Conservator, Underwater Archaeology Branch, Naval History and Heritage Command
It’s never a dull day at Naval History and Heritage Command (NHHC) Underwater Archaeology (UA) Conservation Laboratory especially when a heavily concreted cannon from the suspected wreck site of the 14-gun naval schooner Revenge arrived on May 26, 2017. The cannon, believed to be a six-pounder, was recovered by NHHC archaeologists and divers from Naval Undersea Warfare Center and Explosive Ordnance Disposal Unit 12 Detachment Newport, Rhode Island, as part of a multi-year collaborative effort to survey and research the wreck site.
When the cannon arrived at NHHC, conservators immediately placed it in a sodium carbonate solution to help inhibit further corrosion development and begin the desalination process. This first phase of treatment involves the diffusion of salts out of the artifact into the solution. Soluble salt removal is crucial to ensure chloride-triggered corrosion does not occur after treatment and conservators will regularly monitor the chloride levels in solution during this phase to know exactly how much salt is being removed.
Artifacts recovered from a marine environment are often covered in thick concretions just like the cannon. These concretions form a hard, solid mass over time as the artifact corrodes and interacts with sediment, marine life, and other particulate in the water. Concretions can help protect and preserve the artifact underwater and can sometimes contain other small artifacts embedded within the concretion layers. To remove concretions, conservators frequently use small pneumatic tools and proceed slowly and carefully, layer by layer without harming the artifact surface or any other artifacts within the concretion layer.
Before cleaning, conservators carefully documented and photographed the cannon. During documentation, conservators observed what appeared to be a few pieces of twisted fiber and
possible textile protruding from the concretion at the cannon’s cascabel end, so we focused our cleaning efforts in this general area. Before the day was out, we had uncovered two pieces of rope wrapped around the cascabel neck and a curved metal fragment embedded in the concretion at the filet. We do not yet fully understand the original configuration of the rope, textile and metal fragment or its purpose. Archaeologists and conservators will continue to conduct research and discuss throughout the cleaning process, which will hopefully yield more conclusive evidence as to the identity of the shipwreck.
Mechanically cleaning large artifacts takes time and patience, but as archaeological conservators, we know that this time is well spent, because the end product will be a well-preserved artifact that can shed light on the story of the schooner Revenge, as well as bring the Navy’s history to the public. This cannon’s story is just beginning so stay tuned for updates on the conservation of this unique Navy artifact!